A switch device has been widely applied in various circuits, which functions to turn on and turn off the circuits. When contacts of the switch device are disconnected, an arc is generated and a plasma arc having a column as a conical surface is generated from the combustion at the cathode spot. Especially in a high-voltage circuit, the arc generated by the switch is extremely intense.
When the switch is in an ON status, the switch device should have a lower resistance to allow a rating current to pass through and produce no excessively high temperature. In a process of disconnecting the switch contacts, the arc-extinguishing process needs to be performed, so that the switch contacts are disconnected resolutely. The switch device in the prior art usually adopts oil, sulfur hexafluoride (SF6), air, semiconductor, or vacuum for arc-extinguishing. Different arc-extinguishing media have different characteristics and corresponding switch structures. As the vacuum switch has smaller gaps, higher voltage-resistant capability, lower arc voltage, higher current breaking capability, lower power wear, and longer electrical endurance, the vacuum switch has been widely applied in various power circuits.
A core member of a vacuum switch tube is a vacuum arc-extinguishing chamber, and vacuum switch contacts in the vacuum arc-extinguishing chamber are key members of the vacuum arc-extinguishing chamber. The performance of the vacuum switch contacts decides the performance of the vacuum switch tube. Therefore, how to improve the performance of the vacuum switch contacts is a key point for improving the performance of the vacuum switch tube.
In the vacuum switch tube in the prior art, the vacuum contacts are usually cylinders. A magnetic member and a conductive member are disposed in each contact body. When the vacuum switch tube is disconnected, a contact area of contacts at two ends of the vacuum switch tube gradually decreases, until only one contact point is left between the contacts. At the same time, a contact resistance gradually increases, such that a temperature of an area where the contact point is located gradually rises. Once the temperature is higher than a melting point of the contact point, the contact point is melted, evaporated, and ionized. The metal vapor maintains the discharging in vacuum, so as to generate a vacuum arc. At this time, the key point of the successful current breaking is that an insulation recovery speed at the gaps of the contacts is higher than a transient recovery voltage speed at the gaps of the contacts after the crossing zero of the arc current, such that re-ignition does not occur and the current breaking is successful. During the current breaking in the vacuum arc-extinguishing chamber, the metal vapor released by the arc diffuses rapidly during the crossing zero of the arc current and is condensed instantly upon encountering the contacts or surface of a shielding case. Therefore, the influencing factors such as size, material, or form of contacts, gap between contacts, density of the metal vapor generated during current breaking, and density of charged particles need to be designed properly. Generally speaking, a desirable vertical magnetic field formed between contacts depending on the magnetic members can accelerate arc-extinguishing, which has excellent performance of insulation recovery after arcing.
However, the structure of vacuum contacts in the current vacuum switch tube still has problems such as an electric field concentration, insufficient voltage resistant capability, and higher re-ignition possibility during high-voltage breaking, which fails to satisfy the demand of a higher voltage circuitry. Especially, with the wide application of higher voltage transmission circuitries in the electric power equipment, the higher requirement for the voltage resistant capability of the vacuum switch tube is proposed. How to design a vacuum switch tube with a higher voltage resistant capability to satisfy the demands of higher voltage circuitries has become an urgent technical problem currently.